The memory will be offered in a 4 Hi-stack form factor, resulting in a capacity of 4GB per HBM2 chip. There will be two versions:
By combining four stacks over a 4096-bit HBM2 bus, video card makers will be able to deliver cards with up to 16GB HBM2.H5VR32ESM4H-20C is a 2Gbps chip with 256GB/s bandwidth per stack H5VR32ESM4H-12C is a 1.6Gbps chip with 204GB/s bandwidth per stack
Source: TPU